File:Wormstone (heavily bioturbated quartzose sandstone) (Mazomanie Formation, Upper Cambrian; riverside cliff, western side of the St. Croix River, northeast of Lookout Point, Minnesota, USA) 2 (18814916720).jpg

Wormstone (heavily bioturbated quartzose sandstone) in the Cambrian of Minnesota, USA.

This outcrop consists of quartzose sandstones of the Mazomanie Formation, a shallow marine siliciclastic succession in the Upper Cambrian of the Upper Mississippi Valley, USA. Cross-bedding and Skolithos trace fossils are common here. Intraclastic sandstone horizons are also present.

The bed with the moth-eaten appearance shown above is a quartzose sandstone with numerous burrows (trace fossils). It appears to be consistent with descriptions of "wormstone" in the literature. Wormstones have been previously documented and described in Cambrian sandstone successions of the Upper Mississippi Valley (e.g., Emrich, 1966; Ostrom, 1987; Eoff, 2008).

Stratigraphy: Mazomanie Formation, upper Tunnel City Group (formerly the Franconia Sandstone), Sunwaptan Stage, Upper Cambrian, ~491-493 Ma

Locality: riverside cliff exposures along the western side of St. Croix River, below a rest stop along Rt. 95 between mileposts 101 and 102, just northeast of Lookout Point, north-northeast of the town of Stillwater, Minnesota, USA (45° 05’ 03.80" North, 92° 47’ 10.33" West)

References cited:

Emrich, G.H. 1966. Ironton and Galesville (Cambrian) sandstones in Illinois and adjacent areas. Illinois State Geological Survey Circular 403. 55 pp.

Eoff, J.D. 2008. Sequence-stratigraphic context of Cambrian extinctions: sedimentary facies and trilobite faunas of the Tunnel City Group, Upper Mississippi Valley. Ph.D. dissertation. University of Oklahoma. Norman, Oklahoma. 666 pp.